$OpenBSD: patch-util_h,v 1.1 2017/05/08 01:02:16 espie Exp $
dude, it's not even constant

Index: util.h
--- util.h.orig
+++ util.h
@@ -149,7 +149,7 @@ struct error : exception {
     { };
    
    template<typename T>
-   error &operator <<(const T &s) const t_no
+   error &operator <<(const T &s) t_no
      { msg.append (s); return *this; };
 };
 
